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A Probe-Fed Patch Antenna with a Step-Shaped Ground Plane for 2.4 GHz Access Point
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A Probe-Fed Patch Antenna with a Step-Shaped Ground Plane for 2.4 GHz Access Point

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This Letter demonstrates a new design of a probe-fed patch antenna with a modified antenna ground, and a constructed prototype ideal for applications in a 2.4-GHz WLAN access point is presented. The …

This Letter demonstrates a new design of a probe-fed patch antenna with a modified antenna ground, and a constructed prototype ideal for applications in a 2.4-GHz WLAN access point is presented. The antenna has a thick air substrate for broadband operation and is fed by an inclined probe pin at the edge of the patch bent portion. The antenna ground comprises different portions and is in the shape of a step. With the proposed probe feed and ground configuration, good impedance bandwidth with VSWR below 1.5 over the 2.4 GHz WLAN band can be obtained. In addition, good broadside radiation characteristics have also been observed.

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  • 1. Schultz, Composite medium with simultaneously negative permeabil- ity and permittivity, Phys Rev Lett 84 (2000), 4184 – 4187. 7. R. Marques, F. Mesa, J. Martel, and F. Medina, Comparative analysis of edge- and broadside-coupled split ring resonators for metamaterial design-theory and experiments, IEEE Trans Antennas Propagat 51 (2003), 2572–2581. 8. A. Garcia-Lamperez and M. Salazar-Palma, Dual band filter with split-ring resonators, IEEE MTT-S Int Microwave Symp Dig, San Francisco, CA (2006), 519 –522. 9. F. Falcone, T. Lopetegi, J.D. Baena, R. Marques, F. Martín, and M. ´ Sorolla, Effective negative- stop-band microstrip lines based on com- plementary split ring resonators, IEEE Microwave Wireless Compon Lett 14 (2004), 280 –282. 10. J. Bonache, I. Gil, J. Garcia-Garcia, F. Martin, Novel microstrip bandpass filters based on complementary split-ring resonators, IEEE Trans Microwave Theory Tech 54 (2006), 265–271. 11. J.-S. Hong and M.J. Lancaster, Microstrip filters for RF/microwave applications, Wiley, New York, 2001. 12. J.D. Baena, J. Bonache, F. Martín, R. Marques, F. Falcone, T. Lope- ´ tegi, M.A.G. Laso, J. García, I. Gil, and M. Sorolla, Equivalent circuit models for split ring resonators and complementary split ring resona- tors coupled to planar transmission lines, IEEE Trans Microwave Theory Tech 53 (2005), 1451–1461. © 2008 Wiley Periodicals, Inc. A PROBE-FED PATCH ANTENNA WITH Figure 1 (a) Geometry of the proposed probe-fed patch antenna with a A STEP-SHAPED GROUND PLANE FOR step-shaped ground plane for 2.4-GHz WLAN operation. (b) Side view of 2.4 GHz ACCESS POINT the proposed antenna. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] Fa-Shian Chang,1 Yung-Tao Liu,2 Saou-Wen Su,3 and Jui-Hung Chou3 1 Department of Electronics, Cheng Shiu University, Kaohsiung County, 83347, Taiwan which makes it very difficult to well match the antenna to imped- 2 Department of Electrical Engineering, R.O.C. Military Academy, ance bandwidth within VSWR of 2. In addition to the use of a short Fengshan 83059, Taiwan probe pin, the matching mechanism in these studies also demon- 3 Network Access Strategic Business Unit, Lite-On Technology strates some modification to the structure of the antenna feed. Corporation, Taipei County 23585, Taiwan; Corresponding author: susw@ms96.url.com.tw These designs include the use of a bevel-feed transition [1], a cylinder-feed transition [2], a T-shaped probe feed [3], an L- shaped probe feed [4], an edge-fed patch with an L-shaped ground Received 26 May 2008 [5], a ridge-shaped ground [6], and so forth. In this letter, we introduce a new design of a probe-fed patch antenna capable of ABSTRACT: This letter demonstrates a new design of a probe-fed broadband operation. The antenna is backed by a step-shaped patch antenna with a modified antenna ground, and a constructed proto- type ideal for applications in a 2.4-GHz WLAN access point is pre- ground plane and can be fed by a long probe pin at one of the patch sented. The antenna has a thick air substrate for broadband operation radiating edges. Simply by tuning the probe-pin length, good and is fed by an inclined probe pin at the edge of the patch bent por- tion. The antenna ground comprises different portions and is in the shape of a step. With the proposed probe feed and ground configuration, good impedance bandwidth with VSWR below 1.5 over the 2.4 GHz WLAN band can be obtained. In addition, good broadside radiation characteristics have also been observed. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 139 –141, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 24019 Key words: probe-fed patch antennas; WLAN antennas; access-point antennas 1. INTRODUCTION Many patch antennas utilizing thick air substrates have been de- veloped and studied to achieve impedance bandwidth exceeding 10% defined by 2:1 VSWR or 5% by 1.5:1 VSWR for broadband operation [1– 6]. Among these researches, a short probe pin of the probe feed is mostly employed in conjunction with various match- Figure 2 Measured return loss for the design prototype of various ing mechanism. That is because for patch antenna with such thick probe-pin lengths. [Color figure can be viewed in the online issue, which air substrate, using a long probe pin can cause large inductance, is available at www.interscience.wiley.com] DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 1, January 2009 139
  • 2. For matching the input impedance of the patch antenna, the length of the probe pin was carefully tuned. When a thick air substrate is utilized for the radiating patch, large inductance intro- duced by the probe pin may occur, which can be compensated for additional capacitive reactance arising between the vertical plate (of the ground) and the patch bent portion and between the inclined plate and the bent portion. Thus, the probe pin of the probe feed can be relatively long in this study, compared with the short probe pin used in broadband patch designs reported in [1– 6]. The related results will be elaborated more in the next section. 3. EXPERIMENTAL RESULTS AND DISCUSSION On the basis of the antenna configuration shown in Figure 1, a few prototypes have been constructed and experimentally studied. Fig- ure 2 shows the measured return loss for the design prototype of Figure 3 Measured input impedance for the design prototype of various various probe-pin lengths (d). It is first seen that with d equal to 8 probe-pin lengths. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] mm, good impedance bandwidth defined by 1.5:1 VSWR (14 dB return loss) can be obtained and reaches 140 MHz (2370 –2510 MHz), easily covering the 2.4 GHz band. The sum of d and L impedance matching over frequency band with 1.5:1-VSWR band- (patch length) also corresponds to a half wavelength of the center width of about 6% can be obtained. Several design prototypes have operating frequency at 2442 MHz targeted in this study. In addi- been built, and a design example aimed for operation in the 2.4 tion, compared with a short probe pin, usually 2% wavelength of GHz (2400 –2484 MHz) WLAN band has been implemented too. the center operating frequency, used for broadband patch antenna The proposed antenna is designed for access-point applications in designs [1– 6], the probe pin of 8 mm here is relatively long and the WLAN environment. Details of the antenna design are de- about 6.5% wavelength at 2442 MHz. Notice that when the probe- scribed, and experiment results are discussed. pin length d changes from 5 to 9 mm, the thickness of the air substrate slightly increases from 8 to 11 mm. In general, with an 2. ANTENNA DESIGN increase in d, the antenna operating frequency moves to lower Figure 1(a) shows the geometry, in detail, of the proposed antenna frequencies, where the behavior is the same as that a thicker for operation in the 2.4 GHz band. The radiating patch is in the substrate can result in a lower frequency band as reported in [5]. shape of a rectangle with the dimensions 54 mm (L) 60 mm (W) The measured input impedance, including real (resistance) and and has a small bent portion (4 mm in length) at one of the patch imaginary (reactance) parts, for the antenna of various probe-pin radiating edges. The antenna ground plane is bent three times into lengths (d) is shown in Figure 3. It can be seen that for operating a step-shaped structure and consists of four portions: two horizon- frequencies of interest at about 2442 MHz, the curve of imaginary tal plates, one vertical plate, and one inclined plate, all with the part is closest to 0 with the real-part curve approaching 50 when same width of 80 mm. The angle between the inclined (5 mm in a near optimal value d of 8 mm is chosen. length) and horizontal (60 mm in length) plates is 135°. In the Figure 4 gives the measured radiation patterns of the E-plane center of the inclined plate , below a via hole is located a 50- (x-z cut) and H-plane (y-z cut) at 2442 MHz for the constructed SMA connector of the probe feed. In this case, the probe pin prototype studied in Figure 2 with probe-pin length d 8 mm. (length d) of the probe feed is inclined at an angle of 45° [see Fig. Measurements at other frequencies in the 2.4 GHz band were also 1(b)]. The radiating patch is edge-fed by this inclined probe feed, taken, and the results were similar radiation patterns as those and the probe pin is coplanar with the patch bent portion. The plotted here. In the x-z cut was seen cross-polarization radiation thickness of the air substrate is set to be 10 mm in this study, which below about 20 dB in the E-plane patterns for the frequencies is about 0.08 times the free-space wavelength at 2442 MHz, the over the 2.4 GHz band; as for H-plane patterns in the y-z cut, the center frequency of the 2.4-GHz WLAN band. cross-polarization radiation is below about 15 dB. The measured Figure 4 Measured radiation patterns at 2442 MHz for the patch antenna studied in Figure 2 with the length of the probe pin equal to 8 mm. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] 140 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 1, January 2009 DOI 10.1002/mop
  • 3. ACCURATE DESIGN OF A COMPACT SUPERCONDUCTING MICROSTRIP FILTER Huili Peng,1 Xubo Guo,1 Shichao Jin,1 Yunlong Piao,1 Xiaoping Zhang,1 Bin Wei,1 Baoxin Gao,2 and Bisong Cao1 1 Department of Physics, Tsinghua University, Beijing, People’s Republic of China; Corresponding author: guoxb05@mails.tsinghua.edu.cn 2 Department of Electrical Engineering, Tsinghua University, Beijing, People’s Republic of China Received 26 May 2008 ABSTRACT: This article presents a six-pole high-temperature super- conducting (HTS) filter at 2.5 GHz with a compact size of 10 mm 15 mm on MgO substrate. Twin-spiral resonators with high simulation ac- Figure 5 Measured peak antenna gain against frequency. [Color figure curacy are used in the design procedure. EM simulations verify that the can be viewed in the online issue, which is available at www.interscience. filter response is insensitive to the variations of the cell sizes and the wiley.com] substrate parameters. The untuned measurement of the HTS filter at 70 K shows a high performance. The minimum return loss is 14.7 dB with- out any tuning. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol peak antenna gain is presented in Figure 5, and the peak-gain level Lett 51: 141–144, 2009; Published online in Wiley InterScience (www. is seen to be about 8 dBi. interscience.wiley.com). DOI 10.1002/mop.24018 4. CONCLUSION Key words: HTS filter; microstrip; accurate design A patch antenna fed by an inclined probe pin with a step-shaped ground plane has been proposed, and several prototypes have been 1. INTRODUCTION studied. The impedance matching with VSWR below 1.5 of the High-temperature superconducting (HTS) thin films with ex- antenna for WLAN operation in the 2.4 GHz band can easily be tremely low surface resistance have enabled compact and excellent obtained. The measured results show that although a long probe bandpass filters, which exhibit very low insertion loss, steep band- pin is in use, large probe inductance is well compensated for edges, and high out-of-band rejection. These attractive perfor- additional capacitive coupling arising between the vertical and mances are of great help to improve the sensitivity and selectivity inclined plates of the ground and the patch bent portion. The of communication systems, such as wireless and satellite commu- proposed patch antenna along with good radiation characteristics is nications [1–5]. However, the measured responses of HTS filters suitable for WLAN access-point antennas, especially for the use in usually deviate from the designed results due to the fabrication panel antennas. errors and the variations of the substrate properties [6 – 8]. Thus, tuning is usually a routine procedure to produce a high-perfor- REFERENCES mance HTS filter. As tuning is a time-consuming and repetitious 1. F.S. Chang and K.L. Wong, A broadband probe-fed patch antenna for work, researchers have made great efforts to produce high-perfor- a DCS base station, Microwave Opt Technol Lett 30 (2001), 341–343. mance HTS filters without tuning [9, 10]. 2. F.S. Chang and K.L. Wong, A broadband probe-fed planar patch Spiral resonator has been known to have several advantages, antenna with a short probe pin and a conducting cylinder transition, including compact size, good simulation accuracy, and insensitiv- Microwave Opt Technol Lett 31 (2001), 282–284. ity to the tolerance of fabrication procedures and substrate param- 3. C.L. Mak, K.F. Lee, and K.M. Lu, Broadband patch antenna with a T-shaped probe, IEE Proc Microwaves Antennas Propagat 147 (2000), eters [11–15]. In this article, we choose a half-wavelength twin- 73–76. spiral resonator to design a high-performance HTS filter. The 4. S.L. Yang and K.M. Luk, Wideband folded-patch antennas fed by linewidth of the resonator is 100 m, so that a compact six-pole L-shaped probe, Microwave Opt Technol Lett 45 (2005), 352–355. filter can be created on a 10 mm 15 mm MgO substrate. The EM 5. F.S. Chang and K.L. Wong, Broadband patch antenna edge-fed by a simulations verify that the filter performance is insensitive to the coplanar probe feed, Microwave Opt Technol Lett 31 (2001), 287–289. variations of the cell sizes and the substrate parameters. In addi- 6. J.W. Zhang, S.S. Zhong, and Q. Wu, Large-bandwidth patch antenna tion, the photolithography process was carefully carried out, and with ridge-shaped ground plate, Microwave Opt Technol Lett 48 there is no defect observed in the filter pattern. As a result, the (2006), 487– 488. measured results of the HTS filter show a high performance without any tuning. © 2008 Wiley Periodicals, Inc. 2. FILTER DESIGN PROCEDURE The layout of the six-pole microstrip filter is shown in Figure 1. Half-wavelength twin-spiral resonators with six turns are used in the design, which occupy a size of only 1.1 mm 5.05 mm. The linewidth of the resonator is 100 m, and the space between the tracks is 100 m. We use an MgO substrate with a thickness of 0.51 mm and a relative dielectric constant of 9.73. The total area of the six-pole filter is 15 mm 10 mm. The filter is designed by the general procedure of coupled- resonator filters [16]. The required coupling coefficients according DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 1, January 2009 141